1. Field of the Invention
The invention relates to a cathode ray tube, more particularly to a color cathode ray tube, and most particularly to an internal magnetic shield which is a part of a color cathode ray tube.
2. Description of the Related Art
FIGS. 1 to 4 illustrate conventional color cathode ray tubes. Hereinbelow is explained an internal magnetic shield as a part of a color cathode ray tube.
FIG. 1 is a longitudinal cross-sectional view of a conventional shadow-mask type color cathode ray tube 700.
The illustrated color cathode ray tube 700 is comprised of an electron gun 709 emitting electron beams 710, a funnel 708 which has a length in a direction of a longitudinal center line of the color cathode ray tube 700 and is open at one end and in which the electron gun 709 is located, a face panel or a screen 707 which is open at one end and connected to the funnel 708 such that the funnel 708 and the face panel 707 define a closed space therein, a fluorescent film 706 adhered onto an inner bottom of the face panel 707, an internal magnetic shield 701 which is located in the space and which is open at opposite ends such that electron beams 710 emitted from the electron gun 709 pass therethrough and reach the fluorescent film 706, a mask frame 703 fixedly adhered to the internal magnetic shield 701 and extending towards the face panel 707 from a distal end of the internal magnetic shield 701, a shadow mask 702 located in the space in facing relation with the fluorescent film 706 and supported by the mask frame 703, stud pins 705 arranged on an inner wall of the face panel 707, hook springs 704 each fixed at one end on an outer wall of the mask frame 703 and detachably engaged at the other end to the stud pin 705, and a deflecting yoke 711 located around the funnel 708.
FIG. 2 is a backward perspective view of the internal magnetic shield 701, the shadow mask 702 and the mask frame 703 with portions broken away for clarity.
As illustrated in FIGS. 1 and 2, the internal magnetic shield 701 has a flange portion 701a at one end closer to the face panel 707, and the mask frame 703 also has a flange portion 703a at one end remoter from the face panel 707. The flange portions 701a and 703a are fixed to each other, and hence, the internal magnetic shield 701 and the mask frame 703 are fixed to each other such that the mask frame 703 extends towards the face panel 707 from the internal magnetic shield 701.
As is obvious in view of FIGS. 1 and 2, a distal end or the flange portion 701a of the internal magnetic shield 701 is located remoter from the face panel 707 than the shadow mask 702, that is, located closer to the electron gun 709 than the shadow mask 702.
FIG. 3 is a longitudinal cross-sectional view of a conventional aperture grill type color cathode ray tube 900.
The illustrated color cathode ray tube 900 is comprised of an electron gun 909 emitting electron beams 910, a funnel 908 which has a length in a direction of a longitudinal center line of the color cathode ray tube 900 and is open at one end and in which the electron gun 909 is located, a face panel or a screen 907 which is open at one end and connected to the funnel 908 such that the funnel 908 and the face panel 907 define a closed space therein, a fluorescent film 906 adhered onto an inner bottom of the face panel 907, an internal magnetic shield 901 which is located in the space and which is open at opposite ends such that electron beams 910 emitted from the electron gun 909 pass therethrough and reach the fluorescent film 906, a mask frame including first frames 903B fixed to the internal magnetic shield 901 and second frames 903A fixed to the first frames 903B, an aperture grill 902 located in the space in facing relation to the fluorescent film 906 and supported by the second frames 903A, stud pins 905 arranged on an inner wall of the face panel 907, hook springs 704 each fixed at one end on an outer wall of the second frame 903A and detachably engaged at the other end to the stud pin 905, and a deflecting yoke 911 located around the funnel 908.
FIG. 4 is a backward perspective view of the internal magnetic shield 901, the aperture grill 902, the first frames 903B and the second frames 903A with portions broken away for clarity.
As illustrated in FIGS. 3 and 4, the internal magnetic shield 901 has a flange portion 901a at one end closer to the face panel 907. The first frames 903B are fixed on the flange portion 901a, and the second frames 903A are fixed across the first frames 903B in a direction perpendicular to a direction in which the second frames 903B extend.
As is obvious in view of FIGS. 3 and 4, a distal end or the flange portion 901a of the internal magnetic shield 901 is located remoter from the face panel 907 than the aperture grill 902, that is, located closer to the electron gun 909 than the aperture grill 902.
The conventional color cathode ray tubes 700 and 900 illustrated in FIGS. 1 to 4 are designed to include the internal magnetic shields 701 and 901 to prevent that the electron beams 710 and 910 deflected by the deflecting yokes 711 and 911 in a predetermined direction are further deflected by external magnetic field such as earth magnetism in a wrong direction. To this end, the internal magnetic shields 701 and 901 are generally designed to be composed of ferromagnetic substance and to magnetically shield the electron beams 710 and 910 by surrounding orbits of the electron beams 710 and 910 to prevent the electron beams 710 and 910 from being unpreferably influenced by external magnetic fields.
As mentioned earlier, the distal ends of the internal magnetic shields 701 and 901 in the conventional color cathode ray tubes 700 and 900 are located behind the shadow mask 702 and the aperture grill 902, that is, located remoter from the face panels 707 and 907 than the shadow mask 702 and the aperture grill 902. As a result, both a space between the shadow mask 702 and the fluorescent film 706 and a space between the aperture grill 902 and the fluorescent film 906 are not magnetically shielded.
Accordingly, in the shadow mask type color cathode ray tube 700 illustrated in FIGS. 1 and 2, the electron beams 710 are influenced by external magnetic fields in a space between the shadow mask 702 and the fluorescent film 706, and hence, deflected in a wrong direction. As a result, the fluorescent film 706 receives the electron beams 710 at a location other than a desired location, and hence, a color other than a desired color is produced from the fluorescent film 706.
In the aperture grill type color cathode ray tube 900 illustrated in FIGS. 3 and 4, since the first and second frames 903A and 903B have almost no magnetic shielding effects, the electron beams 910 are influenced by external magnetic fields in a space between the distal ends or flange portion 901a of the internal magnetic shield 901 and the fluorescent film 906. As a result, the electron beams 910 are deflected in a wrong direction, and the fluorescent film 906 receives the electron beams 910 at a location other than a desired location, and hence, a color other than a desired color is produced from the fluorescent film 906.
Since the aperture grill type color cathode ray tube 900 has a wider space not magnetically shielded than the shadow mask type color cathode ray tube 700, the color cathode ray tube 900 is more harmfully influenced by external magnetic fields than the color cathode ray tube 700.
A conventional color cathode ray tube was designed to additionally include an external magnetic sensor, a landing compensation coil and so on so as to cancel influence exerted by external magnetic fields. As a result, the conventional color cathode ray tube was accompanied with problems of an increase in a size, a weight and the number of parts.
For instance, Japanese Unexamined Patent Publication No. 10-261369 has suggested a cathode ray tube capable of canceling influence exerted by external magnetic fields. The suggested cathode ray tube is designed to include a skirt portion extending from a shield. The skirt portion includes a first portion bent so as to extend in parallel with an aperture grill, a second portion inclined in a certain angle from the first portion, and a third portion welded to an outer surface of a frame.
However, the cathode ray tube suggested in the Publication is accompanied with a problem that the skirt portion has a complicated structure, and hence, it would take much time and much cost to fabricate the skirt portion.
It is an object of the present invention to provide a cathode ray tube which is capable of magnetically shielding external magnetic fields which would harmfully influence electron beams, without additional parts such as an external magnetic sensor or a landing compensation coil.
There is provided a cathode ray tube including (a) an electron gun, (b) a funnel which is open at one end and in which the electron gun is located, (c) a face panel which is open at one end and connected to the funnel such that the funnel and the face panel define a closed space, (d) an internal magnetic shield which is located in the space and which is open at opposite ends such that electrons emitted from the electron gun pass therethrough and reach the face panel, (e) a mask frame which internally supports the internal magnetic shield, and (i) a shadow mask which is located in the space in facing relation with the face panel and which is supported by the mask frame. The internal magnetic shield has an edge facing to the face panel. The edge has a closed cross-section and has a projecting portion at least partially projecting from the edge towards the face panel. The projecting portion has a distal end closer to the face panel than a distal end of the shadow mask.
For instance, the cross-section of the edge is a rectangular one.
It is preferable that the edge wholly projects towards the face panel.
It is preferable that the edge has a rectangular cross-section, and the projecting portion projects from the edge at corners of the edge.
It is preferable that the cathode ray tube includes an aperture grill in place of the shadow mask.
It is preferable that the internal magnetic shield has a longitudinal cross-section of a truncated rectangular pyramid.
It is preferable that the cathode ray tube is a color cathode ray tube.
There is further provided a cathode ray tube including (a) an electron gun, (b) a funnel which is open at one end and in which the electron gun is located, (c) a face panel which is open at one end and connected to the funnel such that the funnel and the face panel define a closed space, (d) an internal magnetic shield which is located in the space and which is open at opposite ends such that electrons emitted from the electron gun pass therethrough and reach the face panel, (e) a mask frame which internally supports the internal magnetic shield, and (f) a shadow mask which is located in the space in facing relation with the face panel and which is supported by the mask frame, the internal magnetic shield having an edge facing to the face panel and at least partially being in level with a distal end of the shadow mask.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
As mentioned earlier, the cathode ray tube in accordance with the present invention is designed to include the internal magnetic shield having a projection portion which projects beyond the shadow mask or the aperture grill towards the face panel. The projection portion magnetically shields external magnetic fields which would deflect electron beams in a wrong direction, ensuring it no longer necessary to additionally prepare a compensator such as an external magnetic sensor or a landing compensation coil.
As an alternative, the cathode ray tube in accordance with the present invention is designed to include the internal magnetic shield having an edge facing to the face panel and at least partially being in level with a distal end of the shadow mask. The internal magnetic shield magnetically shields external magnetic fields which would deflect electron beams in a wrong direction, ensuring it no longer necessary to additionally prepare a compensator such as an external magnetic sensor or a landing compensation coil.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.